The present invention relates to an intake system for an internal combustion engine, and more specifically to an intake system including an intake port for increasing incylinder gas motion such as tumble or swirl.
Gas motion in engine cylinder such as tumble or swirl is one of important factors to achieve stable combustion of diluted air/fuel mixture in a spark ignition internal combustion engine. Accordingly, engines of some types require an intake system which can increase incylinder gas motion in wider engine operating region.
A published Japanese Patent Application Kokai Publication No. 2002-54535 shows a gas motion control valve to increase incylinder gas flow by closing a part of the section of an intake port with a gas motion control valve. For tumble, for example, the gas motion control valve is disposed in a lower part of the intake port, and arranged to strengthen the intake air stream alongside the upper side of the intake port. A published Japanese Patent Application Kokai Publication No. H06(1994)-159079 shows an intake system including a partition dividing an intake port into upper and lower halves, and a gas motion control valve closing the lower half of the intake port, to increase a tumble ratio.